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How far do the jet needles pull out of the needle jets?

  • Thread starter Thread starter isaac
  • Start date Start date
I

isaac

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Hey ya'll. It's been a while. Hopefully no catastrophes have befallen anyone. I've torn up my pants a couple times but otherwise good to go.

Anyhoo, I've yanked the carbs on my '82 GS850GL because the powerband was just acting so weird. It pulls really unlinearly. It bogs like hell down low, then slowly winds out, then for about a thousand revs up top (est - the tach is broken) it has a wicked power surge, then falls off right afterward. It has significantly less power at full throttle than at 3/4 throttle as well. The air filter is new.

I'd pulled the carbs before and cleaned them out what I thought was pretty well (used all the same techniques that'd worked fine on the '82 GS750) but the problem is there nonetheless.

So I was messing with them to see if I could figure out at least what was up with the lack of full throttle power. I stuck my finger on the plunger and pressed it up and the needle wouldn't even pull all the way out of the bores. I'm kinda wondering if these carbs had been screwed with before. It's definitely nowhere close to fully exposing the end of the needle jet.

So is it supposed to pull all the way out? Do these needles have adjustable steps? Does shimming them help a lot? Thanks!
 
When the carbs are still assembled, the needles will not come completely out of the holes. This keeps them aligned to they can go back down. However, the slide should go up virtually all the way to the top. Depending on the model, it might stop with about 1/8 inch or so still in the bore.

Pull the tops off the carbs and check the diaphragms carefully. If they appear to be good (no holes or tears), check to see that the needles move freely in the jets. Assemble them very carefully, making sure that the tab on the diaphragm is lined up with the notch in the carb body.

How far out are the mixture screws turned? Start with them about 2 turns out. Check all your vacuum hoses for cracks and leaks.

Do you still have stock air box and mufflers? Or are you running pods and a header? If so, have you re-jetted to match?

As you can see, there are still quite a few details that might need to be addressed, and I am sute others will find more items for you to check.
 
If you inherited the problem and it's carb related, it could be anything.
I doubt there's anything wrong with the jet needle operation.
Your performance description makes me think intake leak(s) first. Does the bike idle significantly higher once warmed up?
 
Mine does! Actually, It surges, then returns to normal after a good rap on the thottle. Thats an intake leak, eh? Are there gaskets, or just the boots 'tween the carbs and cylinder head?
 
Mike_H said:
Mine does! Actually, It surges, then returns to normal after a good rap on the thottle. Thats an intake leak, eh? Are there gaskets, or just the boots 'tween the carbs and cylinder head?
Click to expand...
Most common intake leaks are the manifold o-rings, if you have them, or the manifolds. If you're lucky, it may be loose manifold clamps.
 
The thing's never really idled per se, but that could just be an adjustment problem. It'll run great with the throttle cracked just barely, but won't idle on its own.

Anyway, The boots are super tight. They're so tight I have to push the carbs on with my feet while bracing against the bar at the back of the bike.

Anything else that could cause the wierd running?
 
An intake boot air leak is still the most likely explanation. There's an o-ring that's likely "perished", as the Brits say.

The problem:
http://cycleorings.com/intake.html

The solution:
http://bwringer.com/gs/intakeorings.html

The fact that you have such a tough time getting the carbs off and on indicates that the boots are hardened and likely cracked. Every GS needs new intake boots by now. Replace yours ASAP.

And yes, an intake air leak or any overly lean condition is a dangerous problem that you cannot ignore or wish away. It must be corrected or the exhaust valves will eventually be destroyed. I know this through bitter, terrible, expensive experience with a GS850 acting exactly like yours...
 
The guy who sold me the bike (in pieces) had all new parts including boots so those are good to go, but I think the seals may have been bad. I did what i've been told not to do, which is use an RTV sealant on them to be sure, and things got a lot better.

It now starts instantly instead of with a LOT of screwing with the throttle and cranking for a minute and sometimes even needing to spray gas in there. It immediately settles at a great stable idle and the choke does what it should now instead of just being some random switch.

The powerband is still a little unsmooth, with a dip early on, but muuuuch improved over before. It now has a lot wider powerband before falling off. It could still use some more juice at full throttle but otherwise good to go. Thanks for the help. If things change I'll update.
 
I'm not sure who told you not to use sealant, but it can cretainly help tremendously till you get the necessary parts to fix the problem permanently.
I restored my friend's GS450. It had terrible leaks at the boots. I sealed them up with silicone sealant and he's riding the bike two years and 6000 miles later with no problems.
 
I'm one of the members who say don't use sealant. Sealant is not a good fix.
Sure, you can get lucky. I also understand some of us may have a budget to work with. We do what suits us.
I always recommend the correct fix to whatever the problem is. Experience says this is the way you should maintain a bike. Intake leaks should be fixed correctly, not bandaged. In most cases, this "fix" will just result is wasted labor, which can be just as valuable as the money involved. Plus, the performance may/will suffer.
Not trying to lecture here, but reading the ending of this topic may unfortunately persuade others to try this temp fix. Especially when it gets endorsed. That's not the way to repair an intake leak.
I thought this should be said. :)
 
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